This application is based on Application No. 2002-33919, filed in Japan on Feb. 12, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection control apparatus of an internal combustion engine, and particularly, to an air/fuel ratio feedback control of the internal combustion engine.
2. Description of the Related Art
In a fuel injection control apparatus of an internal combustion engine, there is known an air/fuel ratio control in which the feedback control is conducted in accordance with an output signal from an O2 sensor. In the feedback control, normally, when the state of the output signal from the O2 sensor is a lean state, a computing operation that would increase injection quantity is performed, and when the state of the output signal of the O2 sensor is in a rich state, a computing operation that would reduce injection quantity is performed.
FIG. 4 is a block diagram showing a construction of a fuel injection control apparatus of an internal combustion engine according to the conventional technique. In FIG. 4, reference numeral 1 denotes an O2 sensor, and 2 a feedback controlling means. The feedback controlling means 2 consists of: a feedback determination means 3 for making determination whether the feedback is being performed and for making judgement between the rich state and the lean state, on the basis of the output signal from the O2 sensor 1; a rich-side gain calculating means 4 and a lean-side gain calculating means 5 for calculating a gain on the basis of the determination result obtained by the feedback determination means 3; and a fuel injection quantity calculating means 6 for calculating a fuel injection quantity obtained by multiplying the gain from the gain calculating means and for outputting it. Reference numeral 7 denotes an injector driving means, which drives an injector on the basis of the output from the fuel injection quantity calculating, means 6.
Incidentally, in the above-described fuel injection control apparatus of the internal combustion engine according to the conventional technique, when the feedback control is performed in accordance with the output signal from the O2 sensor, it is necessary that deviation from the target value is minimized. Therefore, the feedback gain is set to such a value that would not cause a rapid change. However, in the O2 feedback control of the internal combustion engine, it is expected that the control is started in the state where there is a large gap between the air/fuel ratio at the time of starting the feedback and the target ratio for the feedback control, depending on the load conditions. Therefore, there is a problem in that it takes a lot of time to reach a stable feedback state from the control start in the case where only a normal feedback gain is prepared.
The present invention has been made to solve the above-described problem and to provide a fuel injection control apparatus of an internal combustion engine, in which the time necessary for the feedback to reach a stable feedback state from the start of the control is reduced to achieve rapid transition to the stable state, thereby enabling effective reduction of the harmful components in exhaust gas.
According to the present invention, there is provided a fuel injection control apparatus of an internal combustion engine, comprising: an air/fuel ratio detector for detecting an air/fuel ratio of exhaust gas of the internal combustion engine; and a feedback controller for conducting feedback control of the fuel injection quantity supplied to the internal combustion engine on the basis of an output signal from the air/fuel ratio detector. The feedback controller performs the feedback control in a manner such that a feedback gain set at the time of starting the feedback control, which is used for imparting operation constant for performing the feedback control in the period from the time of starting the feedback control until an optimum air/fuel ratio is reached, is set to a value larger than that of a feedback gain set for the normal operation period, which is used for imparting operation constant for performing the feedback control in a stable state so that the feedback gain is changed between the time of starting the feedback control and the normal operation period.
Thus, the feedback gain is changed between the time of starting the feedback control and the normal operation time, in performing the feedback control. Therefore, the transition from the air/fuel ratio at the time of starting the feedback control to the target air/fuel ratio is quickly achieved, thereby enabling effective reduction of harmful components in exhaust gas. Additionally, at the time of starting the feedback control, a feedback gain being different from that set for the normal operation time is employed to control a fuel injection quantity, to thereby reduce the time to reach a stable air/fuel ratio.